Getting "error: Module has no attribute" when a 'try' block catching AttributeError

[brettcannon]

• Are you reporting a bug, or opening a feature request? bug
• Please insert below the code you are checking with mypy,
  or a mock-up repro if the source is private. We would appreciate
  if you try to simplify your case to a minimal repro.

        try:
            # os.confstr("CS_GNU_LIBC_VERSION") returns a string like "glibc 2.17".
            version_string = os.confstr("CS_GNU_LIBC_VERSION")
            assert version_string is not None
            _, version = version_string.split()
        except (AssertionError, AttributeError, OSError, ValueError):
            # os.confstr() or CS_GNU_LIBC_VERSION not available (or a bad value)...
            return None
        return version

• What is the actual behavior/output? "error: Module has no attribute "confstr"
• What is the behavior/output you expect? No warning as the try block captures AttributeError
• What are the versions of mypy and Python you are using? mypy 0.750, Python 3.7.4
• What are the mypy flags you are using? (For example --strict-optional) None specifically (using https://github.com/pre-commit/mirrors-mypy)
• If mypy crashed with a traceback, please paste
  the full traceback below.

(You can freely edit this text, please remove all the lines
you believe are unnecessary.)

[ilevkivskyi]

From mypy point of view this is the same as:

try:
    42 + "no"
except TypeError:
    pass

Putting this to even more extreme what if a user has

try:
    main()
except Exception:
    fail_gracefully()

Should mypy just show no errors in the whole program? I think no. There were some discussions about supporting checked exceptions, but even if this will be ever supported, it will be likely only for user-defined exceptions, not for builtin ones.

Realistically this will be never supported, so I would propose to close this unless someone disagrees. For now you can put # type: ignore[attr-defined] there.

[JukkaL]

Yeah, this looks too complicated to support in any generality.